As described in Japanese Unexamined Patent Application Publication No. 2004-71956, an exposed copper (Cu) interconnection, which was exposed by an etching step, an ashing step, and a subsequent washing step, can easily be oxidized. Ordinary, as a pretreatment of a step for foaming upper interconnection layers, a reduction treatment is conducted in a state where a substrate is heated using a reducing gas including NH3 and the like or an inactive gas in order to remove the oxidized portion of the copper (Cu) interconnection, or the copper oxide is removed by a sputtering method using argon (Ar) plasma.
However, when a reducing gas and an inert gas are used to conduct the reduction treatment under heating, an interlayer insulating film containing fluorine and carbon as its main elements is damaged. When the sputtering method using argon (Ar) is conducted, the resputtered copper (Cu) is deposited on a side wall of the interlayer insulating film, which results in deteriorating the characteristic of a device. In addition, argon (Ar) has a low energy transfer efficiency against copper (Cu), therefore, the copper oxide (CuO or CU2O) cannot be efficiently removed. On the other hand, argon (Ar) has a high energy transfer efficiency against, especially, fluorine and carbon, which structure the interlayer insulating film, therefore, there is such a problem that argon (Ar) damages the interlayer insulating film. In a barrier film forming process which is conducted after the reduction treatment, a sputter (PVD) method is often used. However, the sputter method results in delivering further damage to the side wall of the interlayer insulating film.
From the viewpoint described above, there is the need to develop a reduction treatment method for interconnections which can minimize damage to an interlayer insulating film.